The wafering process is necessary in the semiconductor industry because semiconductor devices are fabricated on flat surfaces. Bulk semiconductor material such as Si, SiC, and GaAs are grown as long cylindrical crystals. In order to minimize device size and maximize the surface area available for device fabrication, these cylindrical ingots must be sliced into thin wafers.
Several techniques have been employed to slice semiconductor ingots into wafers. Rotary ID saws are common for softer materials. ID saws use an abrasive impregnated disc to slice one wafer at a time from large ingots. However, kerf loss and cutting efficiency of ID saws are not suitable for extremely hard materials such as SiC. Therefore, wire based slicing is prevalent in hard materials.
A common technique in these applications is slurry based wire slicing. Steel wire is used to carry abrasive particles suspended in slurry to the cutting surface. This technique is often quite slow. Also, the efficiency of the consumable abrasive slurry is low resulting in high cost of operation.
Another popular technique uses abrasive impregnated wire. This technique is often faster and the waste of abrasive particles is minimized as they are bonded to the wire. However, the surface quality of the produced wafers is poor. Saw marks are formed and must be lapped away.
Other slicing techniques use a multi-stage slicing process. First, the ingot is rotated and sliced until the wafers are held together by only a small central section at the axis of rotation. Then rotation stops and the center section is cut away conventionally. This results in very high quality surfaces with the exception of a protruding deformity in the center of each wafer. This deformity must be lapped away.
Previously, composite metal wire with vapor deposited SiC and a boron coating was developed, such as the abrasive wire disclosed in U.S. Pat. No. 4,139,659. The wire developed under this patent offered improvements over the preceding art. However, for cutting extremely hard, brittle materials, such as a silicon carbide or sapphire, wire fixed with a so-called super-abrasive such as diamond, is required.
Additionally, electrodeposition wire comprising abrasives attached to a wire core wire have been developed. Such an abrasive wire is disclosed in “Development of Spiral Chip-Pocket Wire Tool Electrodeposited Diamond Grains”, Journal of the Japan Society for Precision Engineering, 62(2):242, 1996. However, the manufacturing cost of the electrodeposition abrasive wire is high since it takes a long time to bond the abrasives by electrodeposition. Further, the abrasive wire cannot be made long enough for large multi-wire cutting machines, which require lengths of more than 50 km.
Abrasive wire using a resin as the bonding material has also been developed. Such a resin bonded abrasive wire and manufacturing method is disclosed in U.S. Pat. Nos. 6,070,570 and 6,463,921. However, the resin bonded abrasive wire does not produce satisfactory results with respect to the abrasion resistance, mechanical strength, heat resistance, and cutting ability.
As such, a need currently exists for an improved abrasive wire and method of its use for cutting hard brittle surfaces. A need also exists for a slicing technique that will optimize as-cut surface quality and increase slicing efficiency.